Multiple fluid heat pipe

ABSTRACT

A heat pipe having a fluid conduit, a first working fluid, having a first boiling point, disposed in the fluid conduit, and a second working fluid, having a second boiling point being different than the first boiling point, disposed in the fluid conduit. The first and second working fluids are disposed in the fluid conduit of the heat pipe such that during operating heat from the hot body causes the first working fluid to vaporize while the second working fluid remains in liquid phase. The vaporized first working fluid then carries the second working fluid through the fluid conduit to thermally transfer the heat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/609,805, filed on Sep. 14, 2004. The disclosure of the above application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to heat pipes and, more particularly, relates to a heat pipe employing multiple fluids for improved efficiency and operation.

BACKGROUND OF THE INVENTION

Heat pipe heat exchangers are well known in the field of heat recovery and dehumidification. Heat pipes rely on a phase change process to absorb heat by evaporation and release heat by condensation, transferring large amounts of heat energy with very little difference in temperature.

Heat pipes typically comprise a condenser and an evaporator connected to each other in a closed system. The typical heat pipe comprises an enclosed tube system having one end forming an evaporator portion and having another, somewhat-cooler and lower-pressure end forming a condenser portion.

In operation, liquid refrigerant present in the evaporator portion is heated by the environment, vaporized, and rises into the condenser portion. In the condenser portion, the refrigerant is cooled by the environment, is condensed with the release of heat, and is then returned to the evaporator portion. The cycle then repeats itself, resulting in a continuous cycle in which heat is absorbed from the environment by the evaporator and released by the condenser.

Heat pipe heat exchangers are generally made into two sections that are inserted, each in one of two air streams, where there is a temperature differential between the two air streams. The air streams are preferably in close proximity to each other and preferably flow in opposite directions. The flow of the refrigerant in heat pipes can be induced by passive techniques such as gravity flow, capillary action, thermal pumping, and thermo-syphoning.

However, the usefulness of heat pipes is limited in cases where a hot object is positioned above a cold object. In such case, the natural tendency for hot fluid to rise and cold fluid to sink tends to limit the operation of the heat pipe. That is, a hot object positioned relatively above a cold object may heat the fluid within the heat pipe; however, the hot fluid naturally desires to rise or remain adjacent the higher positioned hot object. Likewise, the cold fluid naturally desires to sink or remain adjacent the lower positioned cold object. Thus, the operation of heat pipes is limited when used with hot objects positioned above cold objects.

Accordingly, there is a need in the relevant art to provide a heat pipe system that is capable of operating between higher positioned hot objects and lower positioned cold objects. Furthermore, there exists a need in the relevant art to overcome the disadvantages of the prior art.

SUMMARY OF THE INVENTION

According to the principles of the present invention, a heat pipe having an advantageous construction and method of use is provided. The heat pipe having a fluid conduit, a first working fluid, having a first boiling point, disposed in the fluid conduit, and a second working fluid, having a second boiling point being different than the first boiling point, disposed in the fluid conduit. The first and second working fluids are disposed in the fluid conduit of the heat pipe such that during operating heat from the hot body causes the first working fluid to vaporize while the second working fluid remains in liquid phase. The vaporized first working fluid then carries the second working fluid through the fluid conduit to thermally transfer the heat.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view illustrating a multiple fluid heat pipe according to the principles of the present invention;

FIG. 2 is an enlarged cross-sectional view illustrating a vaporized plug of a first working fluid; and

FIG. 3 is a perspective view illustrating a bundled array of the multiple fluid heat pipes of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

According to the prior art, certain problems occur in the efficient transfer of a thermal load when a hot body to be cooled is located over or above the cold body. That is, in order to accomplish such cooling of the hot body, fluid would flow against its natural tendency (i.e. heat rises and cold sinks).

Typically, a heat pipe is a vacuum vessel containing a relatively small amount of working fluid. The vessel's inner surface is constructed or treated such that the working fluid covers the entire inner surface of the vessel as a thin layer. The vessel is initially evacuated and, thus, it only contains the liquid working fluid on the inner surface and the vapor phase of the fluid throughout the inner volume.

The amount of heat exchange a heat pipe can handle can be enormous. However, it is usually limited by the ability of the liquid layer to counter flow the heat exchange. Classically, heat pipes fail when the liquid layer is dried out at the source of heat. This is particularly so when the liquid layer has to fight gravity to return liquid to a hot region above the cold region. Fighting this problem usually drives up the costs significantly, limiting the applications of heat pipes.

However, according to the principles of the present invention, it has been found that an effective way to overcome this problem—namely, the drying of the liquid layer in the heat pipe—is to employ at least two different working fluids within the same heat pipe. As seen in FIG. 1, a heat pipe 10 is illustrated having a generally sealed volume 12. Heat pipe is arranged to have an first end or evaporator 14 and an second end or condenser 16. In some embodiments, evaporator 14 can be disposed at a higher elevation than condenser 16. At least two working fluids 18 and 20, each having a different boiling point, are disposed within volume 12 such that as heat enters evaporator 14, first working fluid 18 vaporizes and produces a slightly higher pressure and further disrupts the equilibrium within volume 12. During this time, second working fluid 20 can remain in its liquid phase. First working fluid 18 (at a slightly higher pressure) is driven within volume 12 due to the variance in internal pressure and/or the presence of a pressure spike. This higher pressure vapor of first working fluid 18 travels to condenser 16 where a lower temperature outside heat pipe 10 causes the vapor to condense giving up its latent heat of vaporization. During this time, as vaporized first working fluid 18 travels along volume 12, a plug 26 (see FIG. 2) is formed within volume 12. Plug 26 serves to rewet the internal surface of volume 12 with second working fluid 20, which at least partly remains in its liquid phase. Plug 26 pushes a portion 30 of second working fluid 20 and distributes it along the internal surface of volume 12, especially those areas that would otherwise be dry, generally indicated at 28 (FIG. 2). Once working fluid 18 and/or 20 condenses at condenser 16, the condensed fluid is then pumped back to evaporator 14 by the capillary forces developed in volume 12.

In other words, first working fluid 18 creates a pressure differential forcing second working fluid 20 into the areas of low pressure. This process keeps the internal surface of volume 12 continually wetted, eliminates dry spots, or hot spots, and thus improves efficiency of heat pipe 10 relative to conventional heat pipes. This continuous cycle transfers large quantities of heat with very low thermal gradients. The operation of heat pipe 10 is passive and, thus, is driven only by the heat that is transferred. This passive operation results in high reliability and long life.

It should be understood that in arrangements where a hot body 22 is located above a cold body 24, working fluids 18 and 20 are driven upward through internal pressure against the force of gravity. This driving force occurs when first working fluid 18, having a lower boiling point relative to second working fluid 20, vaporizes due to the application of heat from hot body 22. This vaporization further rises and in turn carries a portion of second fluid 20, which is still in a liquid phase due to its higher boiling point. Accordingly, a circulating motion and a continuous layer of fluid over the interior of heat pipe 10, namely volume 12, are maintained, thereby enhancing the efficiency of heat pipe 10.

Heat pipe 10 of the present invention can be constructed to have a size that is conducive for use in a bundled array 50, as illustrated in FIG. 3. Bundled array 50 provides a tailorable system for use in various applications. It should be understood that heat pipe 10 may have any dimensions that are conducive to a given applications; however, in some embodiments, it has been found that heat pipe 10 can have an outer diameter of in the range of about 0.015 inches to about 0.50 inches and up to about 10 feet in length. Heat pipe 10 can also be constructed to be flexible.

Working fluids 18 and 20 may include any combination of fluids that provide a desirable boiling point relation therebetween. In some embodiments, working fluids 18 and 20 include Isopropyl alcohol, Methanol, and the like. In some embodiments, working fluids 18 and 20 have boiling points generally in the range of about 5° C. and 100° C.

It should be recognized that the principles of the present invention may find utility in a wide variety of applications, such as solar panels, heat transfer systems for thermal to electric conversion systems, hot water heaters, micro electronics and the like.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

1. A heat pipe comprising: a fluid conduit; a first working fluid having a first boiling point, said first working fluid being disposed in said fluid conduit; and a second working fluid having a second boiling point, said second boiling point being different than said first boiling point, said second working fluid being disposed in said fluid conduit.
 2. The heat pipe according to claim 1 wherein said first working fluid is Isopropyl alcohol.
 3. The heat pipe according to claim 1 wherein said second working fluid is Methanol.
 4. The heat pipe according to claim 1 wherein said first working fluid and said second working fluid each have a boiling point between about 5° C. and 100° C.
 5. The heat pipe according to claim 1 comprising a plurality of said fluid conduits.
 6. A method of using a heat pipe, said method comprising: providing a hot body and a cold body; providing a heat pipe having a first working fluid having a first boiling point and a second working fluid having a second boiling point disposed therein, said second boiling point being different than said first boiling point; and exposing at least a portion of said heat pipe to said hot body and said cold body thereby causing said first working fluid to vaporize from heat from said hot body while said second working fluid remains in liquid phase, said vaporized first working fluid carrying said second working fluid through said plurality of fluid conduit to thermally transfer said heat.
 7. The method according to claim 6, further comprising: positioning said hot body above said cold body.
 8. A heat pipe comprising: a plurality of fluid conduits defining an array; a first working fluid having a first boiling point, said first working fluid being disposed in each of said plurality of fluid conduits of said array; and a second working fluid having a second boiling point, said second boiling point being different than said first boiling point, said second working fluid being disposed in each of said plurality of fluid conduits of said array.
 9. The heat pipe according to claim 8 wherein said first working fluid is Isopropyl alcohol.
 10. The heat pipe according to claim 8 wherein said second working fluid is Methanol.
 11. The heat pipe according to claim 8 wherein said first working fluid and said second working fluid each have a boiling point between about 5° C. and 100° C. 